The invention relates to radiators and more especially to radiators for cooling IC engines, comprising two coolant headers with assemblies of coolant tubes extending between them.
There is a general trend to provide for the desired cooling effect with a radiator of minimum bulk and with small overall dimensions in order to reduce costs. It is more especially these reasons that have led to the abandonment of radiator designs whose headers are joined by tubes of the same cross section arranged in three planes in favor of designs in which these tubes are arranged in two parallel rows with essentially the same air entry area. At the same time the flow cross section of the tubes has decreased and the number of tubes in each of the two rows has been increased with the result that, although there is a high air speed through the radiator and an improved heat transfer to the heat conducting fins, this was at the cost of a greatly increased resistance to flow; furthermore the modifications were not, on balance, able to compensate for the absence of the third tube row because of the following reasons: the decrease in the cross section of the tubes involved an increase in the performance of the coolant pump if the coolant flow rate was to be maintained, and this led to an increase in pressure, more especially at the coolant inlet port of the radiator. The result of both these factors was an increase in price, that is to say on the one hand, of the radiator means itself owing to the heavy duty coolant pump needed and the design of the radiator to withstand greater heads, while on the other hand the operation of the engine became more expensive owing to the lower mileage. This increase in engine running costs was due to the greater power that had to be produced by the engine leading to a high fuel consumption.
A similar disadvantage was to be found in the case of the radiator in accordance with the German specification No. 3,217,836, in which means were provided for controlling the number of tubes of a coolant tube bank through which coolant is able to flow. Since in this case either all the tubes or only a fraction of them were able to carry coolant flowing in one direction, it is necessary for the coolant pump to be designed with a pumping rate to suit the smallest overall tube cross section which is still open, that is to say it had to be made with a performance greatly in excess of normal performance. Much the same applies for the design of the radiator, since it had to be made to suit the minimum free overall tube cross section and the pressures then obtaining in the radiator.